Welding is widely used to bond structures such as pipes in a power plant, a chemical plant, and the like. In some cases, a residual stress is generated in the vicinity of a welded portion that has subjected to welding. When the welded portion is exposed to high temperature water or the like for a long time while a tensile residual stress remains in the welded portion, stress corrosion cracking occurs and therefore a plurality of crack-like flaws are generated on the same plane or at adjacent positions. Ductile fracture or brittle fracture may occur in the structure having the plurality of flaws. In view of this, in order to prevent the above fracture, a fracture load of the structure having the plurality of flaws is calculated. As a method for calculating such a fracture load, for example, a technology disclosed in PTL 1 is known.
PTL 1 discloses that a fracture evaluation apparatus for a pipe includes a setting unit for setting any transverse section to be evaluated, a setting unit for setting a region of a crack existing in the transverse section, a setting unit for setting a neutral axis with respect to a bending moment acting on a pipe, a changing unit for changing a direction of the neutral axis, a calculation unit for calculating a fracture mechanics parameter along a front edge of a crack in the case where the bending moment corresponding to the neutral axis acts, a detection unit for detecting a local maximum of a distribution curve of the fracture mechanics parameter, a selection unit for selecting an evaluation neutral axis in which the local maximum can be a global maximum, and an evaluation unit for evaluating fracture caused by an action of the bending moment corresponding to the evaluation neutral axis, and therefore, in the case where integrity of a pipe is evaluated, excessive maintainability is removed and a realistic and reasonable fracture evaluation technology for a pipe is provided.